<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
		<style type="text/css">
			.width{
				width: 100%;
			}
			.nav{
				background-color: #fff000;
			}
			.nav-a{
				display: block;
				margin: 0 auto;
				padding: 10px 10px;
				border-bottom: 1px solid red;
				color: #fff;
				border-top: 1px solid red;
			}
			.nav-a:first-child { border-top: 0;}
			.nav-a + .nav-a + .nav-a {border-bottom: 0;}
		</style>
	</head>
	<body>
		<h4>无宽度，借助流动性</h4>
		<div class="nav">
			<a href="" class="nav-a">导航1</a>
			<a href="" class="nav-a">导航2</a>
			<a href="" class="nav-a">导航3</a>
		</div>
		<h4>width:100%</h4>
		<div class="nav">
			<a href="" class="nav-a width">导航1</a>
			<a href="" class="nav-a width">导航2</a>
			<a href="" class="nav-a width">导航3</a>
		</div>
	</body>
</html>
